A binary photomask may include glass and chrome features which form a pattern. Light may pass through the clear glass areas and be blocked by the opaque chrome areas. Light that passes through the mask may continue through a lens, which projects an image of the mask pattern onto a wafer. The wafer is coated with a photosensitive film (photoresist), which undergoes a chemical reaction when exposed to light. After exposure, the areas on the photoresist exposed to the light may be removed in a developing process, leaving the unexposed areas as features on the wafer.
The quality of an image produced with a binary mask may be degraded by light from clear areas on the mask diffracting into regions that ideally would be completely dark. A nominally dark region may have light diffracted into it from the adjacent nominally bright regions. Consequently, contrast between bright and dark regions on the imaging plane may be degraded, thereby degrading image quality.